CVE catalog
CVE-2021-21404
syncthing: CVE-2021-21404
- Severity
- High · CVSS 7.5
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H - Published
- Source
- [NVD] · [CVE record]
- EPSS
- 1.97% · Oct 25, 2026
Syncthing is a continuous file synchronization program. In Syncthing before version 1.15.0, the relay server `strelaysrv` can be caused to crash and exit by sending a relay message with a negative length field. Similarly, Syncthing itself can crash for the same reason if given a malformed message from a malicious relay server when attempting to join the relay. Relay joins are essentially random (from a subset of low latency relays) and Syncthing will by default restart when crashing, at which point it's likely to pick another non-malicious relay. This flaw is fixed in version 1.15.0.
Vulnerable and fixed packages
Distribution-reported package versions and fixes. These do not depend on matching against the OpenFactory package catalog.
| Distribution | Package | Release | Version | Status |
|---|---|---|---|---|
| Debian | syncthing | sid | 1.29.5~ds1-5 | fixed |
| Debian | syncthing | forky | 1.29.5~ds1-5 | fixed |
| Debian | syncthing | trixie | 1.29.5~ds1-2 | fixed |
| Debian | syncthing | bookworm | 1.19.2~ds1-1 | fixed |
| Opensuse | syncthing | leap 15.2 | 1.15.1-lp152.2.3.1 | fixed |
| Opensuse | syncthing | tumbleweed | 1.18.2-2.1 | fixed |
| Suse | syncthing | package hub 15 sp2 | 1.15.1-bp152.2.3.1 | fixed |
Fixed-version evidence
| Distribution | Package | Type | Release | Fixed version | Urgency | Origin | Bugs |
|---|---|---|---|---|---|---|---|
| Debian | syncthing | source | sid | 1.12.1~ds1-3 | not yet assigned | Not reported | [986593] |
| Debian | syncthing | source | forky | 1.12.1~ds1-3 | not yet assigned | Not reported | [986593] |
| Debian | syncthing | source | trixie | 1.12.1~ds1-3 | not yet assigned | Not reported | [986593] |
| Debian | syncthing | source | bookworm | 1.12.1~ds1-3 | not yet assigned | Not reported | [986593] |
| Opensuse | syncthing | rpm | leap 15.2 | 1.15.1-lp152.2.3.1 | Not reported | OPENSUSE-SU-2021:0688-1 | Not reported |
| Opensuse | syncthing | rpm | tumbleweed | 1.18.2-2.1 | Not reported | OPENSUSE-SU-2024:11417-1 | Not reported |
| Suse | syncthing | rpm | package hub 15 sp2 | 1.15.1-bp152.2.3.1 | Not reported | OPENSUSE-SU-2021:0713-1 | Not reported |
OpenFactory catalog packages
[openSUSE Tumbleweed]
- [syncthing-relaysrv]Unknown
Source package: [syncthing]
Details (1)
2.1.3-1.1· x86_64 · tumbleweedUnknown · Fixed:
1.18.2-2.1Version impact unknown
dsa · syncthing · opensuse · tumbleweed
- [syncthing]Fixed
Source package: [syncthing]
Details (1)
2.1.3-1.1· x86_64 · tumbleweedFixed · Fixed:
1.18.2-2.1dsa · syncthing · opensuse · tumbleweed
[Debian 12 (Bookworm)]
Source package: [syncthing]
Details (2)
1.19.2~ds1-1· all · bookwormFixed · Fixed:
1.12.1~ds1-3dsa · syncthing · debian · bookworm; dsa · syncthing · debian · 12
1.19.2~ds1-1· all · bookwormFixed · Fixed:
1.12.1~ds1-3dsa · syncthing · debian · bookworm; dsa · syncthing · debian · 12
- [syncthing]Fixed
Source package: [syncthing]
Details (2)
1.19.2~ds1-1+b4· amd64 · bookwormFixed · Fixed:
1.12.1~ds1-3dsa · syncthing · debian · bookworm; dsa · syncthing · debian · 12
1.19.2~ds1-1+b4· arm64 · bookwormFixed · Fixed:
1.12.1~ds1-3dsa · syncthing · debian · bookworm; dsa · syncthing · debian · 12
- [syncthing-discosrv]Fixed
Source package: [syncthing]
Details (2)
1.19.2~ds1-1+b4· amd64 · bookwormFixed · Fixed:
1.12.1~ds1-3dsa · syncthing · debian · bookworm; dsa · syncthing · debian · 12
1.19.2~ds1-1+b4· arm64 · bookwormFixed · Fixed:
1.12.1~ds1-3dsa · syncthing · debian · bookworm; dsa · syncthing · debian · 12
- [syncthing-relaysrv]Fixed
Source package: [syncthing]
Details (2)
1.19.2~ds1-1+b4· amd64 · bookwormFixed · Fixed:
1.12.1~ds1-3dsa · syncthing · debian · bookworm; dsa · syncthing · debian · 12
1.19.2~ds1-1+b4· arm64 · bookwormFixed · Fixed:
1.12.1~ds1-3dsa · syncthing · debian · bookworm; dsa · syncthing · debian · 12
[Debian 13 (Trixie)]
Source package: [syncthing]
Details (2)
1.29.5~ds1-2· all · trixieFixed · Fixed:
1.12.1~ds1-3dsa · syncthing · debian · 13
1.29.5~ds1-2· all · trixieFixed · Fixed:
1.12.1~ds1-3dsa · syncthing · debian · 13
- [syncthing]Fixed
Details (2)
1.29.5~ds1-2· amd64 · trixieFixed · Fixed:
1.12.1~ds1-3dsa · syncthing · debian · 13
1.29.5~ds1-2· arm64 · trixieFixed · Fixed:
1.12.1~ds1-3dsa · syncthing · debian · 13
- [syncthing-discosrv]Fixed
Source package: [syncthing]
Details (2)
1.29.5~ds1-2· amd64 · trixieFixed · Fixed:
1.12.1~ds1-3dsa · syncthing · debian · 13
1.29.5~ds1-2· arm64 · trixieFixed · Fixed:
1.12.1~ds1-3dsa · syncthing · debian · 13
- [syncthing-relaysrv]Fixed
Source package: [syncthing]
Details (2)
1.29.5~ds1-2· amd64 · trixieFixed · Fixed:
1.12.1~ds1-3dsa · syncthing · debian · 13
1.29.5~ds1-2· arm64 · trixieFixed · Fixed:
1.12.1~ds1-3dsa · syncthing · debian · 13
Observed:
References
- [https://ftp.suse.com/pub/projects/security/csaf/opensuse-su-2021_0688-1.json]
- [https://osv.dev/vulnerability/DEBIAN-CVE-2021-21404]
- [https://osv.dev/vulnerability/openSUSE-SU-2021:0688-1]
- [https://osv.dev/vulnerability/openSUSE-SU-2021:0713-1]
- [https://osv.dev/vulnerability/openSUSE-SU-2024:11417-1]
- [https://security-tracker.debian.org/tracker/CVE-2021-21404]
[Debian Security Tracker] · [FIRST EPSS] · [OSV Package Vulnerability Database] · [SUSE security advisories and VEX]